Method for actuating a tool in a well at a given depth and tool allowing the method to be implemented

ABSTRACT

A downhole tool is actuated at chosen well depth by selection of a control element that melts at the chosen depth well temperature. In one form of tool, a fusible pin melts to release spring-loaded jaws which move against an expansion cone to anchor the tool in the well. In another form, a fusible receptacle cover melts to release a quantity of dense fluid under action of gravity. Suitable control elements are formed of bismuth, with lead and zinc.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to downhole working in boreholes, as in the caseof oil or geothermal wells.

2. Background Information

During prospecting and production operations, it is often necessary toanchor a tool in a borehole at a chosen depth. More generally, manytypes of tools are designed to be actuated at a well-determined depth:this is the case, for example, of a cement dump bailer which must bedischarged at the depth at which a well is to be closed off.

The conventional procedure consists in first lowering the tool by meansof a cable to the desired depth determined by the unreeled length ofcable. The tool is then anchored in the production tubing. Then, theactual control of the tool is achieved by repeated pulling exerted fromthe surface via the cable until the failure of one or more pins. Whenthe cable used is an electric cable, it is possible to use explosivemeans controlled electrically from the surface. All prior art systemsare of the abrupt-action type, which is considered to be necessary inthis technique in order to avoid inadvertent triggering of the toolother than at the desired depth.

For traction actuation, the calibration of the fracture pin(s) must bedefined carefully and the tool control operations require the securingof the tool in the well. As regards explosive techniques, which areapplicable only when an electric cable is used, they also require quiterigorous safety precautions well known to those of the art.

Finally, certain wells having a particular configuration oppose the useof conventional downhole tool triggering techniques. This is the case inparticular of wells which exhibit a local restriction beyond which thetool must be triggered. This restriction makes difficult and evenimpossible the passage of a tool equipped with anchoring means. It mayalso be mentioned that the control of a tool by pulling on the cable ispoorly suited to deviated wells.

SUMMARY OF THE INVENTION

The present invention provides a satisfactory solution to theseproblems.

It is thus a primary object of the invention to provide means fortriggering a tool in a borehole which reconciles a soft action mode withas great a reliability as prior art techniques.

Another object of the invention is to provide triggering means which aresoft and yet quite rapid, notably for the control of tools such ascement bailers.

A further object of the invention is to allow the actuation of tools atdepths and/or in wells in which this has hitherto not been possible.

Finally, it is an object of the invention to provide a technique fortriggering a tool in boreholes, capable of being easily adapted in thefield according to requirements.

For this purpose, the invention proposes first of all a method foractuating a tool in a well at a chosen depth.

This method comprises the following operations:

(a) Determining the temperature of the well at the chosen depth.

(b) Equipping the tool with a control element made of a material capableof melting at a tempeature near the temperature thus determined.

(c) Lowering this tool to the desired depth, and waiting there for theactuation of the tool by the melting of the control element.

This technique is effective in every case, but is particularly useful inthe case of wells having a restricted and/or highly deviated passage.

In current embodiments of the method, energy is stored in the tool andis then released by the melting of the control element.

At the present time, it is considered desirable that the meltingtemperature of the material forming the control element be defined withan accuracy of plus or minus 5° C., and preferably plus or minus 2° C.approximately.

In practice, a material is chosen which has a melting temperature equalto or slightly lower than the temperature of the well at the desireddepth. This can be determined by direct measurement using a temperatureprobe or by the measurement or even the estimation of the temperaturegradient along the well. The waiting time to be complied with to obtainthe triggering of the tool is related to the time necessary for thethermal equilibrium between the tool and the well fluid when the toolhas reached the desired depth. It is generally a fraction of this time.

The invention also provides downhole tools allowing the implementationof this method.

In a general definition of such a tool, it comprises, in combination,mechanical means capable of being loaded on the surface for storingenergy, as well as at least one control element melting at apredetermined temperature and whose melting ends said storage.

According to another definition, the tool comprises two parts normallysubject to relative motion, as well as a control element made up of afusible part securing the two parts against said relative motion.

In a first embodiment of the tool, the two parts are subjected torelative motion in relation to each other upon encountering an elasticreturn. The control element comprises a lock such as a fusible pinsecuring the two parts in relation to each other in the tensionedposition of the elastic return.

One of the current requirements in the manipulation of tools loweredinto wells is the anchoring of these tools in the well. It is readilypossible to provide anchoring means by equipping one of the parts withjaws supported movably with axial sliding on a rod terminating in anexpansion cone toward which the jaws are loaded by the elastic return.

The anchoring can thus be obtained without requiring repeated pulling bymeans of the cable or equivalent means.

According to another embodiment of the invention, one of the two partsof the tool forms a receptacle containing the other part againstmovement under the action of gravity. One thus obtains, for example, acement bailer consisting of a receptacle provided with an opening whichcan be closed by a plug.

The applicant has observed that certain special metallic alloysexhibiting all the desired properties for use in wells are capable ofmelting practically cleanly at any chosen temperature between about 45°and 400° C., the temperature accuracy being ±2° C., or better.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear fromthe following detailed description given in connection with the appendeddrawings in which:

FIGS. 1A and 1B represent an anchoring tool according to the presentinvention; and

FIG. 2 represents a cement bailer according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Equipment lowered into oil and/or geothermal wells operates under veryspecific conditions in which it undergoes exceptional pressure andtemperature stresses.

Thus, to actuate a tool in a well it is recognized that it is necessaryto:

equip this tool with an element capable of breaking under awell-determined load, which has to be adjusted,

lower this tool to the desired depth,

anchor it there,

exert repeated pullihng from a distance, generally by means of a cable,until the fracture of said element.

In certain cases, as in the case of cement bailers, it is possible touse explosive means remote controlled by an electric cable from thesurface. The explosion then opens the gate which releases the cement atthe desired depth in the well. In addition to the fact that it has nogeneral application, this exlosive technique has serious drawbacksrelated, firstly, to the existence of the explosion and, secondly, tothe combustion scrap and other debris resulting therefrom.

The present invention offers a very different solution, unknown up tothe present time, for the triggering of tools lowered into oil orgeothermal wells. This solution is based upon the application ofspecific metals or metallic alloys capable of melting at awell-determined temperature definable within a narrow range such as ±5°C., or better, ±2° C.

Although different types of materials may meet this condition, theapplicant presently prefers to use the "fusible" alloys sold by SocieteBraconnot in Paris, France.

By varying the proportions of the elements composing this alloy, it ispossible to define with great accuracy its melting point, which can godown to about 45° C. This material is easily machinable and has meltingproperties sufficiently clean to give satisfaction.

It is known that wells, and notably oil wells, are the scene of atemperature gradient, the temperature increasing on the average by about1° C. every 30 meters. Although this temperature variation is notrigorously linear, it remains substantially monotonic and exhibits, withdepth, only plateaus or small variations. It has been found that thissituation is compatible with the use of the melting of an alloy asdefined above for the release of energy stored on the surface and in thetool.

Under certain circumstances, very precise measurements are made of thetemperature profile of a well as a function of depth, to within 1° C.Independently of precise measurements, for any well, the temperature ofthe well as a function of depth is generally known to within a fewdegrees. When it is desired to actuate a tool in a well at a chosendepth, it is thus possible to determine the temperature of the well atthis depth to within 1° or 2° C.

As previously indicated, the tool is equipped with a control elementmade of a material such as the abovementioned alloy, chosen so that itsmelting temperature is near the temperature of the well thus determinedat the desired depth. The tool is lowered to this depth to awaitactuation by the melting of its control element.

It has also been observed that any tool penetrating into a well does notimmediately acquire the temperature of the well at its location. Thelatency time necessary for the tool to be in thermal equilibrium withthe well when the tool is stopped at a well-determined location iscurrently of the order of ten minutes or so. The fusible material isthus chosen so that its melting temperature is equal to or preferablylower than the temperature of the well at the desired depth. It has thenbeen observed that the melting takes place in a few minutes, therebyactuating the tool.

The energy stored on the surface in the tool can be of various kinds: itmay consist of a hydrostatic pressure difference or the energy of aprecalibrated spring, for example. In the first case, a material isstored in the tool that has a density higher than the density of thefluid filling the well at the desired depth. The fusible control elementwill, by opening a gate, discharge this material from the tool. Theenergy storage is then comparable in this case to the storage of matterand this matter is associated with energy which depends on thedifference in the densities of said matter and of the fluid filling thewell.

This is the case of a cement dump bailer or any other body having adensity higher than that of the fluid in the well. Other examplesinclude sand or gravel.

The invention is applicable to most downhole tools in which it isnecessary to maneuver a liner under difficult conditions or when shocksare detrimental to its operation, which rules out the use of prior artcables. This corresponds to the second case, namely the mechanicalstorage of energy by means of a precalibrated spring or equivalentmeans.

FIGS. 1A and 1B illustrate a first embodiment of the present inventionallowing the anchoring of a tool in a well.

The tool is illustrated inside a production tube CP. It comprises a headbushing 101 equipped at one end with a flange 100 and on the other endwith attachment means 102.

To lower it into the well, the head 101 is fixed to the end of anonconducting cable by means of a setting tool. The body of the tool isotherwise of a generally cylindrical form. Below the element 102, itincludes a solid cylinder 103 followed by another flange 104. Thisflange defines the maximum outer diameter of the tool in its restposition before anchoring.

The shoulder 104 is followed by a conical body 111 which tapers down toa central cylindrical rod 110. At its lower end, the rod 110 is providedwith a flange 112.

On the rod 110 is slidably mounted an annular body member 120 whoseupper part defines an annular recess 121. Into this recess 121 areinserted the feet 122 and 122A of two anchoring elements 123 and 123Awhose other ends form dogs or jaws (operating in extension) 124 and124A.

The insides of the jaws 124 and 124A are flared upwardly. In the restposition, they bear on the beginning of the expansion cone 111.

The bottom of the annular member 120 forms a stop for a spring 130 whichalso bears on the upper shoulder of the flange 112 already mentioned. Inthe rest position of the tool, a pin 140 goes through the rod 110 tosecure the annular member 120 in a position in which the spring 130 isunder compression.

The pin 140 is made of a fusible material according to the invention.

In operation, the tool is lowered to the desired depth after havingplaced therein a pin 140 melting at the corresponding temperature.

After the melting of the pin 140, which takes place after a few minutes,the spring 130 loads the ring 120 upwardly which in turn pushes the jaws124 and 124A so that they are moved outwardly by the cone 111 and engageon the production tubing CP, thus anchoring the tool.

This anchoring function is thus obtained without any shock. Moreover,the means used allow a significant movement of the jaws 124 and 124Abetween their rest position and their anchoring position, whereasgenerally prior-art means were incapable of doing so.

The arrangement according to the invention thus makes it possible toachieve satisfactory anchoring beyond a restriction, owing to the greatrange of movement allowed for the jaws 124 and 124A.

The second embodiment of the invention is illustrated in FIG. 2 in theform of a cement bailer. The head piece 203 is provided with a flange202 and a threaded upward extension 201. The lower end of head piece 203forms a cover 204 perforated at 205. A cylindrical tube 210 is securedinside the cover 204 by a pin 206. A pad 211 secured on the bottom ofthe cylindrical tube 210 by a pin 212 applies a disk 240 against the endof the tube.

This disk 240 is made of a fusible material according to the invention.

In this case also, a tool of this type is capable of differentapplications, notably those consisting in cementing a well beyond arestriction. Furthermore, the use of this cement bailer is faster thanin the prior art where it was often necessary to wait for the cement tobegin solidifying before bringing in another cement bailer to continuethe cementation.

Two examples are given below to illustrate respectively theimplementation of the two tools described.

EXAMPLE 1

Tools as illustrated in FIGS. 1A and 1B have been provided with fusiblepins, one melting at 70° C. and the other at 120° C.

The compositions of the alloys used for the pins were the following:

at 70° C.:

50% bismuth

25% lead

12.5% zinc

12.5% cadmium

at 120° C.:

1% zinc

55% bismuth

44% lead

It was possible to install these anchoring tools under very difficultconditions, namely in a well deviated in depth, equipped with aproduction tubing having an intermediate part of smaller diameter thanthe upper and lower parts. These tools all proved satisfactory, whereasprior art anchoring means could practically not operate.

EXAMPLE 2

A tool according to FIG. 2 was made with, for the part 240, a disk of"ceroben" of 2-mm thickness and 40-mm diameter which melted at 120° C.Its composition was the same as the alloy indicated in Example 1.

In this manner, twelve cement bailers (eleven for cement and one forsand) were placed successively at a depth of about 5000 meters,successfully and very rapidly.

U.S. Pat. No. 4,390,291 gives the composition of alloys melting atvarious temperatures.

Of course, the present invention is not limited to the particular toolsjust described.

Based upon the storage of energy by a spring as used in FIG. 1, it ispossible to provide a fusible pin whose melting will in turn drive asecond stronger pin which will in turn trigger the tool, but with agreater energy, stored for example in a second spring. One thus achievesmechanical amplification to obtain the energy required for triggeringthe tool.

Conversely, instead of the "gate" 240 of the tool in FIG. 2 beingentirely in fusible material, it would also be possible to provide agate loaded to open by means of an elastic return, or simply by gravity,and kept in place by a fusible lock.

The invention can also be applied to other types of tools and inparticular to the downhole placing of fragile electronic instruments orthe downhole actuation of material samplers.

What is claimed is:
 1. A method for actuating a tool in a well at achosen depth, comprising the following steps:determining the temperatureof the well at the chosen depth; equipping the tool with a centralelement comprising a material capable of melting at a temperature nearthe temperature thus determined; lowering the tool into the well to thechosen depth; and maintaining the tool in the well at the chosen depthuntil actuation of the tool by the melting of the control elementmaterial.
 2. A method as defined in claim 1, wherein energy is stored inthe tool in the equipping step and released for actuation of the toolupon the melting of the control element material in the maintainingstep.
 3. A method as defined in claim 1 or 2 wherein the tool isequipped with a control element material that melts at a temperatureequal to or lower than the temperature of the well at the chosen depth;and wherein the tool is maintained at the chosen depth for a waitingtime that is related to the thermal equilibrium time between the tooland the well.
 4. A method as defined in claim 1, wherein the meltingtemperature of the material is defined with an accuracy of ±5° C.
 5. Amethod as defined in claim 4, wherein the melting temperature of thematerial is defined with an accuracy of ±2° C.
 6. A downhole tooldesigned to be actuated in response to the temperature of a well at achosen well depth, comprising:a body member adapted to be lowered into awell at the end of a cable; energy storage means associated with saidbody member for storing energy in said tool prior to lowering said bodymember into said well; and control means comprising a material thatmelts at a temperature near the temperature of said well at said chosendepth and cooperable with said energy storage means for releasing saidstored energy to cause actuation of said tool.
 7. A tool as defined inclaim 6, wherein said energy storage means comprises a movable elementpositioned for movement with respect to said body member between a firstposition and a second position relative thereto; and wherein saidcontrol means comprises a fusible part securing said movable element insaid first position.
 8. A tool as defined in claim 7, wherein saidenergy storage means further comprises biasing means for biasing saidmovable element into said second position; whereby melting of saidfusible part in response to the well temperature at said chosen welldepth will cause said movable element to move to said second positionunder the action of said biasing means.
 9. A tool as defined in claim 8,wherein said body member comprises a rod including an expansion coneportion, said movable element comprises jaws slidably mounted on saidrod, said biasing means comprises a spring urging said jaws toward saidcone portion, and said fusible part comprises a pin locking said jawsaway from said cone portion against the bias of said spring.
 10. A toolas defined in any of claims 6, 8 or 9, wherein the melting material ismade of a metallic alloy capable of melting substantially cleanly at apredetermined temperature between about 45° C. and 400° C., saidtemperature being defined within an accuracy of ±5° C.
 11. A tool asdefined in claim 11, wherein said alloy comprises mainly bismuth, aswell as at least one of the elements lead and zinc.